Multiphoton ionization of hydrogen iodide and molecular iodine using photoelectron spectroscopy
Gu, Yiyun
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https://hdl.handle.net/2142/20103
Description
Title
Multiphoton ionization of hydrogen iodide and molecular iodine using photoelectron spectroscopy
Author(s)
Gu, Yiyun
Issue Date
1993
Doctoral Committee Chair(s)
Eden, James G.
Department of Study
Electrical and Computer Engineering
Discipline
Electrical and Computer Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Electronics and Electrical
Language
eng
Abstract
Hydrogen iodide and I$\sb2$ molecules were studied by time-of-flight photoelectron spectroscopy using multiphoton ionization techniques. At a pumping wavelength of 532 nm, it was concluded that dissociation due to the intermediate repulsive valence states is very strong for both HI and I$\sb2.$ For HI, the dissociative valence states correlate with H($\sp1$S) + I($\sp2$P$\sb{3/2,1/2});$ And for I$\sb2,$ they correlate with I($\sp2$P$\sb{3/2,1/2})$ + I($\sp2$P$\sb{3/2,1/2}).$ As a result, ionization from the ground states of spin-orbit doublets $(\sp2$P$\sb{3/2,1/2})$ of atomic iodine is predominant in the photoelectron spectra. In contrast, photoionization of HI at 355 nm is direct, owing to the absence of the dissociative valence states. Vibrationally resolved spectra were observed for both of the spin-orbit doublets of the HI$\sp+$ ground state (v$\sp+$ = 10 for $\sp2\Pi\sb{3/2}$ and v$\sp+$ = 6 for $\sp2\Pi\sb{1/2})$ and the vibrational constants and anharmonicities were extracted from the data. Tunable laser experiments (567-578 nm) showed a new Rydberg series of I$\sb2$ converging to the excited state of $\rm I\sbsp{2}{+}(\sp2\Sigma\sb{3/2\rm u}).$
At laser intensities of ${\sim}10\sp{13}$ W/cm$\sp2$ and a driving wavelength of 532 nm or 355 nm, above-threshold ionization (ATI) was observed. Because of the strong dissociation at 532 nm for both HI and I$\sb2$, only ATI of atomic iodine was observed. With the 355 nm laser, ATI of HI was observed. Above threshold ionization of I$\sb2$ was also observed at 579.5 nm at laser intensities exceeding ${\sim}10\sp{11}$ W/cm$\sp2$.
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